People looking to become Luthiers (aka Guitar Makers) typically start out as Apprentices or Assistants to a professional Luthier. This way, they get hands-on experience, which is important in such a hands-on profession. Plus, you learn to make guitars that you can then play once they’re done.
Most Luthiers also go through some sort of higher education or online course. Matt Rubendall, a professional Luthier, went to a six-week lutherie school. There, he says, they trained people to work in the big guitar-making factories, like Martin or Taylor.
But he says nowadays, people prefer to spend much more time learning and getting educated to either work for a small guitar shop, start their own Luthier business, or just do it on the side.